Show list of available functions and methods

Description

I see many people (including myself) staring at the editor and asking "what functions are available". This might not be the right way to approach a problem but I see this happening to many people. Actually code completion plays along the same way of thinking.

So I'd like to be able to see the list of all the available functions similar to what F2 does now but also categorized.
Maybe it should have another selector (combo box) where one could select a subject, the subject could be

Perl 5 - string functions

Perl 5 - array functions

Perl 5 - system functions

HTML::Template methods
etc... listing the relevant subjects so if in my project I use HTML::Template then it is listed as one of the subjects

We should probably make this a bit flexible, meaning that we should include some functions from some of the core modules in the list of standard functions e.g. basename() from File::Basename in the "Perl 5 - system functions".

We might even have a list of other things such as "xml" that would describe some of the ways to handle XML in perl.